The shearing, or slitting, of sheet metal has been accomplished in the past in several different ways.
One primary way involves the use of a set of long blades set at a desired shear angle and driven vertically through the material. Shears of this type require large, heavy frames related to one another by precision connections and expensive bearings. Another problem is that it is difficult to set and maintain the proper blade clearance. In addition, the long shear blades are costly to make and regrinding them is an expensive and time consuming process.
Another common apparatus utilizes roller shears which employ round rotary blades supported on arbors. As the material is fed through, the blades shear the material. As in the case of the long blade shears, the support framing, housings, bearings and arbors are difficult to manufacture, expensive, heavy and the equipment as a whole is inconvenient to move from place to place. The rotary blades require precision sharpening and there are severe problems in maintaining appropriate blade clearance so as to achieve precise shearing.
Shearing has also been done manually with hand tools such as scissors, hand shears and reciprocating shears. These devices do not, however, lend themselves to obtaining accuracy or to an acceptable rate of production. In addition, their use is obviously labor intensive.